This invention relates to a material for use as a transparent conductive film comprised mainly of tin oxide, a method for making a transparent conductive film using the same, and the use thereof.
As a material for transparent conductive film, there are known ITO (indium tin oxide), ATO (antimony tin oxide) and the like. These materials are employed as a transparent electrode for liquid crystal display devices, an electrode for solar cells, and an antistatic film for Braun tubes.
As electronic devices are progressing in performance, there is a demand of a transparent conductive film being low in resistivity and high in transparency along with the formation of such a low resistivity film at low temperatures.
There are known a variety of methods of making such transparent conductive films, which can be broadly classified into two groups including a physical film-forming method and a chemical film-forming method. The resistivity of the film depends greatly on the manner of the film formation. Hence, it is important to select a proper method depending on the use of the conductive film.
As set out, for example, in Japanese Laid-open Patent Application No. 2-72549, the ATO film formed according to the physical film-forming method is made at relatively low temperature as having a low resistivity according to a magnetron sputtering technique. On the other hand, according to a chemical film-forming method, there is formed a high strength film with a low resistivity wherein cobalt, nickel or cerium compounds are added to ATO as taught in Japanese Laid-open Patent Application No. 60-220505.
The above-described prior art methods have some problems. With the magnetron sputtering method, the material suffers damages on irradiation of a plasma which is essentially required in the process of the sputtering technique. In addition, it is difficult to appropriately control the compositional ratios in the film, coupled with another disadvantage that a large-scale vacuum apparatus is necessary with a difficulty in coating over a large area.
The film to which cobalt, nickel or cerium compounds are added to ATO as set out in Japanese Laid-open Patent Application No. 60-220505 is based on the concept that the crystallization of the ATO is expedited using the added cobalt, nickel or cerium compound as a firing aid thereby forming a low resistance film. The effect of the above additive is so small that the resistivity is reduced only to an extent of (1.8.about.2.0).times.10.sup.-2 .OMEGA..cm to (8.7.about.9.4).times.10.sup.-3 .OMEGA..cm. Moreover, an additional thermal treatment at temperatures exceeding 500.degree. C. is undesirably necessary.